One of the means of improving oil well production is to increase the permeability of the subterranean formation of interest. The treatment method selected depends upon the type of formation encountered and may involve opening clogged pores, crevices and other flow channels in the formation or fracturing the formation to create cracks which are then propped open with sand or gravel.
In order to fracture stimulate a well, a packer is set above the zone of interest in order to isolate the well casing from extremely high working pressures. Because the packer seals off the annulus between the casing and the tubing string, it is not possible to collect bottom-hole pressure data from the annulus. This leaves two other ways of collecting such data. One is to support a pressure recorder on a wireline and place it in the tubing string near the zone of interest. While this procedure permits collection of bottom-hole pressure data during acid stimulations and during informational or data fracture stimulations in which no sand is introduced, it is not practical during sand fracturing. The pumping of sand proppant at high rates and pressures down the tubing string creates a sandblasting effect which is detrimental to a recorder in the tubing string. Moreover, the presence of a recorder in the tubing string creates a restriction in the tubing, which causes pressure differentials above and below the recorder that can affect the success of the stimulation.
The other way of collecting pressure data is to place the recorder in an isolated joint of the tubing string below a perforated tubing sub. Problems also exist with this method. Collection of bottom-hole pressure data can be carried out during acid stimulations and data fracture stimulations but not during actual fracture stimulations, inasmuch as sand collecting in the dead joint between the recorder and the dead joint interferes with the pressure recording. An added problem is the difficulty in retrieving the recorder through the packed sand after the stimulation operation.
Another area of activity in which it is difficult to collect bottom-hole pressure data is in rod pumping wells, where the use of a pressure recorder on a wireline can interfere with the operation of the pump and movement of the rods.
It would be desirable to be able to collect bottom-hole pressure data in the environments discussed without interfering with the ongoing activity of the operation and without diminishing the accuracy of the pressure recorder. It would also be desirable to accomplish this by relatively simple, economical means which does not require lengthy set-up procedures.